In a conventionally known wireless communication technology, an uplink (also referred to as an “up”) generally means a channel through which data is transmitted from a mobile station apparatus to a base station apparatus when the base station apparatus and the mobile station apparatus communicate with each other in cellular communication or the like. In this uplink, the base station apparatus simultaneously receives signals from various mobile station apparatuses. Therefore, if the levels of reception power from various mobile station apparatuses are equal to each other, the base station apparatus can easily perform reception processing, and excellent reception properties are also achieved. In order to realize this, a method of controlling the transmit power of a signal transmitted by the mobile station apparatus is introduced into a cellular system, and this is referred to as transmit power control (TPC).
A formula used for determining a transmit power value used in the data communication of an uplink that is defined in specifications (non-patent document 1) on next-generation cellular communication (3.9G) is shown below.[Formula 1]PPUSCH(i)=min{PCMAX,10 log10(MPUSCH(i))+PO—PUSCH(j)+α(j)·PL+ΔTF(i)+f(i)}  (1)
In formula (1), PUSCH stands for physical uplink shared channel, and represents a data channel through which data for an uplink is transmitted. PPUSCH (i) represents a transmit power value in the i-th frame. min {X, Y} is a function for selecting the minimum value from X and Y. Po—PUSCH is transmit power on which PUSCH is based, and is a value that is specified by an upper layer. MPUSCH represents the number of resource blocks (RB: a unit used when a terminal accesses a base station) used for transmission in a data channel, and indicates that, as the number of RBs used is increased, the transmit power is increased. In addition, PL represents path loss, and α is a coefficient by which the path loss is multiplied and is specified by the upper layer. ΔTF is an offset value in a modulation scheme or the like, and f is an offset value (a transmit power control value in a closed loop) calculated by a control signal from the base station. Furthermore, PCMAX is the maximum transmit power value, and PCMAX may be physically the maximum transmit power or may be specified by the upper layer.
Next, a formula used for determining a transmit power value used in control data communication is shown below.[Formula 2]PPUSCH(i)=min{PCMAX,P0—PUSCH+PL+h(nCQI,nHARQ)+ΔF—PUCCH(F)+g(i)}  (2)
In formula (2), PUCCH stands for physical uplink control channel, and represents a control channel through which control data in an uplink is transmitted. Although parameters used in formula (2) is approximately the same as used in formula (1), since the number of RBs has been determined in the control data, there is no parameter that depends on the number of RBs. A coefficient by which path loss is multiplied is not set. Here, h is a parameter that is determined by what information is included in data on PUCCH, and an offset value is determined by the type of data. g is an offset value (a transmit power control value in a closed loop) calculated by a control signal from the base station.
Meanwhile, in the next-generation cellular system, as an uplink communication method, DFT-S-OFDMA (stands for discrete Fourier transform spread orthogonal frequency division multiple access, and is also referred to as SC-FDMA: single carrier frequency division multiple access or DFT precoded OFDM) is used. This method has the property of a signal in a single carrier method and a very excellent PAPR (peak to average power ratio) property.
The PUSCH and the PUCCH described above have different frequency bands that are allocated, and although the mobile station apparatus can physically perform simultaneous transmission in the PUSCH and the PUCCH, the simultaneous transmission is not performed in the PUSCH and the PUCCH in the specifications of the next-generation cellular communication (3.9G), in consideration of degradation of the PAPR property caused by performing the simultaneous transmission.
Furthermore, in a more advanced generation (4G), a technology referred to as carrier aggregation is being examined in which systems whose specifications have been specified in 3.9G are caused to function as one system by being used in parallel in a plurality of different frequency bands. This technology has the advantage of more simply enhancing a throughput.
Moreover, the extension of the communication method is being examined, and one of the candidates is a method referred to as a clustered DFT-S-OFDM. In this method, RBs are discretely used although RBs continuous in a frequency region are used in the DFT-S-OFDM method. Since the clustered DFT-S-OFDM is characterized in that discrete RBs are used, the PAPR property is degraded, but the diversity effects of frequency selection can be expected. Furthermore the number of RBs that cannot be used due to restriction of the use of continuous RBs can be reduced.
Non-patent document 1: 3gpp ts 36. 213
FIG. 6 is a diagram showing the configuration of a transmission apparatus based on the specifications of 3.9G. In FIG. 6, a scrambling section 200 scrambles data on the PUSCH. A modulation section 201 performs error correction and digital modulation. A DFT pre-coding section 202 performs pre-coding through DFT. A modulation section 203 modulates data in the PUCCH. A spreading section 204 performs data spreading specified by the specifications. A selection section 205 performs selection based on which one of the PUSCH and the PUCCH is transmitted.
A resource map section 206 allocates data to be transmitted to a subcarriers to be transmitted. An OFDM signal generation section 207 generates an OFDM signal including a guard interval. A RF section 208 is constituted by to a subcarriers to be ranging from a D/A conversion (digital/analog conversion) section to an antenna. The RF section 208 includes a transmit power control section A, and a control section 209 performs transmit power control.
The following formula is a formula for determining transmit power in 3.9G.[Formula 3]PPUSCH(i)=min{PCMAX,10 log10(MPUSCH(i))+PO—PUSCH(j)+α(j)·PL+ΔTF(i)+f(i)}  (3)PPUCCH(i)=min{PCMAX,P0—PUCCH+PL+h(nCQI,nHARQ)+ΔF—PUCCH(F)+g(i)}  (4)
In the circuit configuration shown in FIG. 6, transmit power control is performed such that the transmission apparatus uses the transmit power control section A to control transmit power and that consequently, the transmit power can be expressed by formula (3) or formula (4).
In W-CDMM used in 3G, as the output power of the transmission apparatus, an output power of about −50 dBm to 24 dBm is required. When this value is applied to a 3.9G system without being processed, a variable region of about 74 dB is determined in the transmit power control section A. Furthermore, in 3.9G, the frequency bandwidth of transmission is variable.
For example, if the 3.9G system is a system that can be used from 1 RB to 100 RB, an input power to an amplifier is varied by 20 dB. If an output power of −50 dBm to 24 dBm is required for all the RBs, the transmit power control section A totally needs a variable region of 94 dB. Further, this becomes a serious problem when a larger number of RBs are used by the transmission apparatus as in the carrier aggregation.
Another problem is that, since the number of RBs used is different, it is likely that a bit resolution required for the D/A conversion section is affected. For example, a difference of 20 dB in the input power corresponds to a resolution of 6 bits to 7 bits. Furthermore, when, in the configuration shown in FIG. 6, the PUCCH and the PUSCH are transmitted at the same time, it is impossible to perform transmit power control in each physical channel, and it is also impossible to perform transmit power control in units of the carrier aggregation.
The present invention has been made in view of the foregoing conditions, and an object of the present invention is to provide a transmit power control method and a transmission apparatus which can perform transmit power control to minimize an impact on a circuit in a system of a variable transmission bandwidth.